One form of method and apparatus for checking the uniformity of a tire for a wheel of a vehicle such as a motor vehicle, as are to be found in DE 197 31 486 and EP 0 884 547, provide that a respective interferogram of the surface of the tire is produced prior to and after a change in the tire inflation pressure, using coherent radiation. The interferograms are displayed and information regarding tire defects which are possibly present is obtained from a comparison of the corresponding images. To record the interferograms the wheel carrying the tire to be checked is fitted as by clamping on a conventional wheel balancing machine as is typically used for example for motor vehicle wheels. Then, a checking head arranged on the balancing machine is moved towards the tire until reaching a predetermined checking distance therefrom, to record the interferograms. The interferograms in respect of the surface of the tire are then recorded in a segment-wise manner. Whenever the recording of a respective checking segment is concluded the wheel is further rotated by an amount corresponding to the length of the respective checking segment, by operation of the balancing machine. That procedure is repeated until the entire tire has been checked in that fashion.
The corresponding tire checking apparatus comprises a balancing machine, a compressed air device for altering the tire inflation pressure, a checking head, a positioning device for the checking head, a computer and a control device for the balancing machine in order to further rotate the wheel by an amount corresponding to the length of a checking segment. While a commercially available balancing machine is supplied together with a computer and a control device for setting the angular speed of the balancing machine, the air pressure device for altering the air pressure in the tire, the checking head and the positioning device for the checking head are items of additional equipment which have to be further provided by a workshop in order to be able to carry out that tire checking method.
In addition, tire uniformity measuring machines have long been known, with which it is possible to ascertain the spring characteristics of a tire in a condition of rolling under load, in three mutually perpendicular axial directions. Defects or structural flaws in the tire being investigated can also be determined from the tangential, radial and lateral forces which are ascertained in that way. Such a tire uniformity measuring machine is relatively large and, because of the amount of space that it requires, it is generally not to be found in most workshops so that it is usually not available to a motor vehicle tire fitter. Nonetheless, for safety reasons, it is desirable for such checking methods to be available prior to fitting a new or used tire, so that a possible defect on the tire can be discovered or substantially ruled out in good time.